Vortex Formation in a Plasma Interacting with Neutral Flow

Recently, it has been observed that there exists a class of vortices which rotates in the opposite direction to E×B drift (referred to as anti‐E×B vortex). This result suggests that a predominant force other than electric field is acting on ions. It is found that momentum transport and resultant force generation through the interaction between ions and neutral flow play an essential role on anti‐E×B vortex formation. The existence of inward neutral flow, which drives the ions in the anti‐E×B direction, has been confirmed using a newly‐developed high‐resolution laser induced fluorescence (LIF) spectroscopy system.